1. Field of the Invention
This invention pertains to the general field of construction and excavating equipment attachments intended to enable a user to perform other functions than those for which the equipment is designed. In particular, it provides a new and improved crane attachment that quickly converts a conventional loading machine, such as a skid steer loader, a backhoe, or a front-end loader, into a crane useable for lifting and moving objects within the perimeter of a work site.
2. Description of the Prior Art
People have been using cranes and hoisting devices to lift and move heavy objects for centuries. During the last few decades, though, movable motorized equipment has become indispensable for the efficient and competitive performance of construction and similar work. Accordingly, machinery such as front-end loaders, fork lifts, backhoes and the like have become common place at work sites.
Since this kind of equipment is expensive, manufacturers have from time to time designed accessory attachments that enable the same piece of equipment to be used for more than one function, so as to optimize the use of each machine. For example, attachments are available to transform front-end loaders into fork lifts by removing the standard bucket from its quick-release coupling mechanism and substituting it with a similarly coupled fork attachment. Other common attachments include lifting booms for tractors, graders and bulldozers. Typically, the standard coupling mechanism existing on the equipment is used to ensure the quick and safe engagement and disengagement of the accessory attachment as well.
Various boom attachments have been developed for use in conjunction with front-end loaders and backhoes to provide the function of a crane, normally in the form of a boom that is secured to the working arm or arms of the equipment and a cable with a hook for grabbing and lifting an object. Depending on the configuration of the equipment and the corresponding attachment, a winch with a pulley or sheave at the tip of the boom may also be provided.
For example, as early as 1942, in U.S. Pat. No. 2,301,808 Mosner describes a grader with a boom mounted on its blade frame and extending forward for use as a hoist. A guy cable is provided for adjusting the position of the boom, while a separate hoist cable is used for lifting objects secured to a hook. The boom portion of the grader is not intended to be a separate attachment; rather, it is an integral part of the machine, designed for lifting large objects that cannot be pushed out of the way by the forward motion of the blade of the grader.
U.S. Pat. No. 2,719,730 to Beck (1955) discloses a hydraulic hoist in the form of an attachment for tractors. The hoist is specifically constructed to fit on the back of a tractor for exerting a lifting force directly upwards, such as would be required for tilting a wagon being pulled by the tractor, lifting heavy weights, or pulling fence posts out of the ground. It consists of a hydraulic cylinder and a cable/hook combination. The lift is provided by the vertical expansion of the cylinder.
U.S. Pat. No. 2,770,895 to Rymkevitch (1956) shows a piece of equipment similar to the grader/hoist combination of Mosher, but provided in the form of a quick release attachment. A boom is connected to the frame of the bulldozer and is operated by the hydraulic power normally used to run the blade. No new power connection is required to run the boom, which is used to lift objects attached to its outer end by raising the blade structure that supports it.
In U.S. Pat. No. 3,030,713 (1962), Hendrickson et al. illustrate a material handling machine that features a boom extension for vertical drilling. The equipment is relevant for its use of a boom structure that could be adapted for lifting, but the design is specific for roof bolting in an underground mine environment.
U.S. Pat. No. 3,812,979 to Leihgeber (1974) discloses a lift boom for a front-end loader. The boom is attached to the loader by securing it to the bucket through a system of cables. By lifting and tilting the bucket through the normal power train used during its operation as a loader, the tip of the boom is raised, thereby causing any load attached to it to be lifted.
U.S. Pat. No. 4,200,423 to Sornsin (1980) describes a simpler boom attachment for the bucket of a front-end loader. A relatively light-weight telescopic boom is provided for direct connection to the top of the bucket, so that its motion can be controlled by the operation of the bucket itself. Again, loads are lifted by securing them to the tip of the boom and by tilting the bucket upwards, which causes the rising of the boom and of the load attached to it.
U.S. Pat. No. 4,293,269 to Zook (1981) shows an extension beam for an excavator. It is designed to replace the scoop bucket of the excavator to convert it from a power shovel to a power hoist. By utilizing the same hydraulic power train used to maneuver the scoop, the extension beam can be controlled to adjust its position for operating as a crane. The lifting function is provided by a standard winch/cable combination mounted on the beam attachment.
In U.S. Pat. No. 4,523,684 (1985), Baisden illustrates another crane attachment for replacing the bucket of an excavator arm. A sleeve is mounted on the arm and connected to the hydraulic power train of the backhoe for controlling an extendable boom contained in the sleeve, thus converting the machine into a crane. The boom in turn is fitted with a winch for lifting loads hooked to a cable through a pulley mounted on the outer end of the boom. The reach of the crane can be varied by extending or contracting the telescopically constructed boom.
Finally, U.S. Pat. No. 4,960,359 to Lovitt, Jr. (1990) describes a boom hoist for connection with the standard attachment points of the bucket of a front-end loader. The lifting motion is achieved by the tilt of the boom as the power train normally used to tilt the bucket is utilized to swing the boom upward. Because of the direct coupling of the device to the bucket attachments, it exhibits great maneuverability and control. However, it does not include the cable lifting action that is typical of a crane.
The main objective in the operation of a crane is the ability of the operator to lift and move a load maintaining the center of gravity of the loaded equipment within the area defined by the equipment's points of contact with the ground, normally determined by the two outer wheel axles or, if available, by extended outrigger pads. Secondly, it is important that the crane be easily maneuverable in order to permit the user to reach the object to be lifted and move it to the desired location, which at times may have to be accomplished in tight quarters with no open access. Thus, the usefulness of a crane is measured by its loading power, its reach, and its flexibility in handling material, all of which require mechanical sophistication, which in turn contributes to the high cost of cranes in general. It is because of the great expense associated with even small cranes that accessory attachments for other common types of equipment are developed.
All of the attachments described in the above referenced prior art constitute extensions of the working arms of the equipment to which they are attached; therefore, to the extent that the lifting boom is outside the perimeter of the outer wheels, they dangerously shift the center of gravity toward an unstable condition. As a result, the load that they are capable of lifting is often limited by the stability of the assembly, rather than by the power of the equipment. These attachments normally utilize the working motion of the various equipment components and are therefore limited by the power available to them. In addition, the maneuverability of the attachment becomes integrally related to and dependent upon the maneuverability of the equipment itself, because it becomes a part thereof, thus often inherently lacking the freedom of motion required for the efficient and safe use of a crane.
Therefore, there still exists a need for a new and improved, self-contained, crane structure for quick attachment to the coupling mechanism of a conventional loading machine and designed to minimize these problems. It is to the achievement of these goals that this invention is addressed.